Video encoding method

ABSTRACT

A picture coding method according to the present invention includes: a coding step (S 102,  S 103 ) of coding, picture parameter sets (PPS) to be used for decoding all the pictures (pic) included in a random access unit (RAU) made up of plural pictures and a sequence parameter set (SPS); and a parameter set placement step (S 104 ) of placing, in the random access unit (RAU), the parameter set (PPS, SPS) coded in the coding step (S 102,  S 103 ).

TECHNICAL FIELD

The present invention relates to a picture coding method for coding apicture.

BACKGROUND ART

Recently, with an arrival of the age of multimedia which handlesintegrally audio, video and pixel values of others, existing informationmedia, i.e., newspapers, journals, TVs, radios and telephones and othermeans through which information is conveyed to people, has come underthe scope of multimedia.

Generally speaking, multimedia refers to a representation in which notonly characters but also graphics, audio and especially pictures and thelike are related to each other. However, in order to include theaforementioned existing information media in the scope of multimedia, itappears as a prerequisite to represent such information in digital form.

However, when calculating the amount of information contained in each ofthe aforementioned information media as the amount of digitalinformation, the information amount per character requires 1-2 byteswhereas the audio requires more than 64 Kbits (telephone quality) persecond and when it comes to the moving picture, it requires more than100 Mbits (present television reception quality) per second. Therefore,it is not realistic to handle the vast information directly in digitalform via the information media mentioned above. For example, avideophone has already been put into practical use via IntegratedServices Digital Network (ISDN) with a transmission rate of 64Kbit/s-1.5 Mbit/s, however, it is impossible to transmit video capturedon the TV screen or shot by a TV camera.

This therefore requires information compression techniques, and forinstance, in the case of the videophone, video compression techniquescompliant with H.261 and H.263 standards internationally standardized byInternational Telecommunication Union-Telecommunication StandardizationSector ( ITU-T) are employed. According to the information compressiontechniques compliant with the MPEG-1 standard, picture information aswell as audio information can be stored in an ordinary music CD (CompactDisc).

The Moving Picture Experts Group (MPEG) is an international standard fora compression of moving picture signals and MPEG-1 is a standard thatcompresses video signals down to 1.5 Mbit/s, namely, to compress theinformation included in TV signals approximately down to a hundredth.The quality targeted in the MPEG-1 standard was the medium quality so asto realize a transmission rate primarily of about 1.5 Mbit/s, therefore,MPEG-2, standardized with the view to meet the requirements ofhigh-quality picture realizes a TV broadcast quality for transmittingmoving picture signals with a transmission rate of 2-15 Mbit/s. In thepresent circumstances, a working group (ISO/IEC JTC1/SC29/WG11)previously in the charge of the standardization of the MPEG-1 and theMPEG-2 has standardized MPEG-4 which achieves a compression ratesuperior to the one achieved by the MPEG-1 and the MPEG-2, allowscoding/decoding operations on a per-object basis and realizes a newfunction required by the era of multi media. At first, in the process ofthe standardization of the MPEG-4, the standardization of a codingmethod for a low bit rate was aimed, however, the aim is presentlyextended to a more versatile coding including a coding of movingpictures at a high bit rate and a coding of interlace pictures.Moreover, a standardization of MPEG-4 AVC and ITU H.264 is in process asa next generation coding method with a higher compression rate, jointlyworked by the ITU-T and the ISO/IEC. The next generation coding methodis published under the name of Committee Draft (CD) as of August 2002.

In coding of a moving picture, compression of information volume isusually performed by eliminating redundancy both in spatial and temporaldirections. Therefore, inter-picture prediction coding, which aims atreducing the temporal redundancy, estimates a motion and generates apredictive picture on a block-by-block basis with reference to forwardand backward pictures, and then codes a differential value between theobtained predictive picture and a current picture to be coded. Here,“picture” is a term to represent a single screen and it represents aframe when used for a progressive picture whereas it represents a frameor a field when used for an interlaced picture. The interlaced picturehere is a picture in which a single frame consists of two fields havingdifferent time. For coding and decoding an interlaced picture, threeways are possible: handling a single frame either as a frame, as twofields or as a frame structure or a field structure depending on a blockin the frame.

A picture to which intra-picture prediction coding is performed withoutreference pictures is called I-picture. A picture to which inter-pictureprediction coding is performed with reference to a single picture iscalled P-picture. A picture to which inter-picture prediction coding isperformed by referring simultaneously to two pictures is calledB-picture. Two pictures whose display time is either forward or backwardto that of a current picture to be coded can be selected arbitrarily asreference for coding B-picture. The reference pictures can be specifiedfor each block which is a basic unit for coding and decoding, but theycan be classified as the first reference picture for a reference picturethat is described first in a coded bit stream and a picture that isdescribed later as the second reference picture. However, the referencepictures need to be already coded or decoded as a condition to code ordecode these I, P and B pictures.

A motion compensation inter-picture prediction coding is employed forcoding P-pictures or B-pictures. The motion compensation inter-pictureprediction coding is a coding method applying motion compensation tointer-picture prediction coding. The motion compensation is not a methodto simply predict motions using pixels in the reference pictures but toestimate a motion (to be referred to as “motion vector” hereinafter) ateach part within a picture and improve prediction accuracy by performingprediction that takes the motion vector into consideration as well as toreduce the data amount. For example, the amount of data is reduced byestimating the motion vector for a current picture to be coded andcoding prediction error between a predictive value, which is obtainedafter being shifted for the amount equivalent to the motion vector, andthe current picture. In the case of using this method, information onmotion vectors is required at the time of decoding, therefore, themotion vectors are coded and then recorded or transmitted.

A motion vector is estimated on a block-by-block basis. More precisely,a motion vector is estimated by fixing a block in the current picture,then, shifting a block in the reference picture within a range ofsearch, and finding out a location of the reference block that resemblesa basic block.

FIG. 1 is a block diagram showing the structure of the conventionalpicture coding apparatus.

A picture coding apparatus 900 outputs a coded image signal (to bereferred to as “bit stream”) Str9 which is a bit stream obtained bycoding an image signal Vin on a picture-by-picture basis, and includes amotion estimation unit 903, a motion compensation unit 905, a subtractor906, an orthogonal transformation unit 907, a quantization unit 908, aninverse quantization unit 910, an inverse orthogonal transformation unit911, an adder 912, a picture memory 904, a switch 913, a variable lengthcoding unit 909 and an access point determination unit 902. Eachcomponent such as the motion estimation unit 903 executes the followingprocessing per block or per macroblock that constitutes a picture.

The subtractor 906 calculates a differential value between the imagesignal Vin and a predictive image Pre and outputs the differential valueto the orthogonal transformation unit 907. The orthogonal transformationunit 907 transforms the differential value into frequency coefficientsand outputs them to the quantization unit 908. The quantization unit 908quantizes the frequency coefficients and outputs the quantized values tothe variable length coding unit 909. The inverse quantization unit 910restores the frequency coefficients by inversely quantizes the quantizedvalues and outputs the frequency coefficients to the inverse orthogonaltransformation unit 911.

The inverse orthogonal transformation unit 911 performs inversefrequency transformation on the frequency coefficients outputted fromthe inverse quantization unit 910 into pixel differential values andoutputs them to the adder 912. The adder 912 adds the pixel differentialvalues outputted from the inverse orthogonal transformation unit 911 andthe predictive image Pre outputted from the motion compensation unit905, and generates a decoded image. The switch 913 connects the adder912 and the picture memory 904 so that the picture memory 904 stores thedecoded image generated by the adder 912. The decoded image stored inthe picture memory is simply referred to as “picture” hereinafter.

The motion estimation unit 903 refers to the picture stored in thepicture memory 904 as a reference picture and specifies an image areathat resembles the image signal Vin the most among the referencepictures. Then, the motion estimation unit 903 estimates a motion vectorMV indicating a position of the image area.

The motion estimation unit 903 also identifies a reference picture thatresembles the image signal Vin out of the plural reference picturesusing identification numbers (relative index Idx) for identifying thereference picture.

The motion compensation unit 905 extracts an image area that is the mostapplicable to the predictive image Pre from among the pictures stored inthe picture memory 904 using the motion vector MV and the relative indexIdx. The motion compensation unit 905 then generates a predictive imagePre from the extracted image area.

The access point determination unit 902 instructs the motion estimationunit 903 and the motion compensation unit 905 to code (intra-picturecode) per predetermined unit (random access unit) a predeterminedpicture as a special picture. The special picture here means a picturefrom which the decoding can be started in the stream Str 9. Furthermore,the access point determination unit 902 outputs an access pointidentifier rapp indicating that a picture is the special picture to thevariable length coding unit 909.

The variable length coding unit 909 codes a parameter set PS obtainedfrom outside resources, the motion vector MV, the quantized values, therelative index Inx and the access point identifier rapp, generates astream Str9 in which the coded parameter set is placed only at the headside, and outputs the stream Str9.

FIG. 2 is a structural diagram showing the structure of the stream Str9outputted by the conventional picture coding apparatus 900.

The stream Str9 includes sequentially from the head a synchronous signalsync, a parameter set PS, plural random access units RAU9. Such streamStr9 complies with the ]VT (H.264/MPEG-4 AVC) which is presently inprocess of standardization, jointly worked by the ITU-T and the ISO/IEC.

The parameter set PS is common data equivalent to a header and includesa picture parameter set PPS is equivalent to a header of the picture, asequence parameter set SPS equivalent to a header of a unit with a levelsuperior to a random access unit RAU9. The sequence parameter set SPSincludes a maximum possible number of reference pictures, a picturesize, or the like, whereas the picture parameter set PPS includes a typeof variable length coding (a switching between Huffman coding andarithmetic coding), an initial value in the quantization step, thenumber of reference pictures, or the like.

The random access unit RAU9 includes sequentially from the head asynchronous signal sync and a plurality of coded pictures pic. Therandom access unit RAU9 as such is a single unit including the pluralpictures in the stream Str9 and includes the special picture asmentioned above which can be decoded without depending on otherpictures. Namely, the random access unit RAU9 is obtained by dividingthe stream Str9 into a group of plural pictures including a specialpicture.

The picture pic includes sequentially from the head a synchronous signalsync and a parameter set identifier PSID and plural pieces of pixel datapix.

The parameter set identifier PSID indicates the sequence parameter setSPS and the picture parameter set PPS, which are included in theparameter set PS, to be referred to by the picture pic.

The synchronous signal sync included in the head of the stream Str9, inthe head of the random access unit RAU9 and in the head of the picturepic indicates respectively a section distinguishing the units such asthe stream Str9, the random access unit RAU9 and the picture pic.

Namely, in the picture coding method in which the conventional picturecoding apparatus 900 generates a stream Str9 by coding the image signalVin, a stream Str9 is generated in such a way that the parameter set PSis coded together and then placed at the head side of the stream Str9,whereas plural random access units RAU9, each of which does not includea picture parameter set PPS and a sequence parameter set SPS, followsthe parameter set PS.

When decoding such stream Str9, the picture decoding apparatus refers tothe sequence parameter set SPS and the picture parameter set PPSincluded in the parameter set PS indicated by the parameter setidentifier PSID in the picture pic so as to decode the picture pic.

A conventional stream according to MPEG-2 has a structure different fromthe stream Str9.

FIG. 3 is a structural diagram showing the structure of the conventionalstream according to the MPEG-2.

A stream Str8 according to the MPEG-2 includes sequentially from thehead a synchronous signal sync, a header hed that is common data in thestream Str8 and a plurality of groups of pictures GOP.

The group of picture GOP includes sequentially from the head asynchronous signal sync, a header hed that is common data for the groupof pictures GOP and plural coded pictures pic.

The group of picture GOP as such is a basic unit for coding and is usedfor editing a moving picture and performing random access. The picturepic included in the group of picture GOP is either I-picture, P-pictureor B-picture.

The picture pic includes sequentially from the head a synchronous signalsync, a header that is data common to the pictures pic and plural piecesof pixel data pix.

Namely, in the picture coding method according to the MPEG-2 forgenerating a stream Str8 by coding the conventional image signal Vin, astream Str8 is generated in such a way that the header hed necessary fordecoding the picture pic is included respectively in the heads of thestream Str8, each group of picture GOP and each picture pic.

However, a problem is that the picture decoding apparatus cannot decodefrom a random access point that is a head of the random access unit RAU9in the stream Str9 (i.e. random access) in an attempt to startperforming random access, for example, in the case where the parameterset PS cannot be obtained since the stream Str9 is read out from themiddle, as the parameter set PS is placed in one place at the head sideof the stream Str9 according to the conventional picture coding methodas described above, employed by the picture coding apparatus 900.Namely, the picture decoding apparatus cannot decode the picture picproperly because the corresponding picture parameter set PPS andsequence parameter set SPS are not found.

More precisely, the stream Str9 cannot be decoded from the middle whenthe picture decoding apparatus has read in the stream Str9 from themiddle under the circumstance where the stream is incessantlytransmitted as in a case of broadcasting or delivery.

In the case where the stream Str9 is recorded on a recording medium suchas a tape or a disk, the picture decoding apparatus firstly has to readthe parameter set PS placed in the head of the stream Str9 on therecording medium and then start reading the stream Str9 from the randomaccess point in the attempt to start performing random access for thestream Str9. That is to say that the picture decoding apparatus has toshift the position of reading the data from the head of the stream Str9to the random access point, and thereby, a prompt random access cannotbe operated since the shifting time becomes a waiting time for therandom access.

In the case where the recording medium is a tape, it is apparent thatthe waiting time is very long, and even if the disk is capable ofhigh-speed reading, the waiting time may be prolonged to severalseconds, which cannot be ignored.

The picture decoding apparatus can perform random access for each groupof picture GOP on the stream Str8 generated using the picture codingmethod according to the MPEG-2 by using the header hed in the group ofpicture GOP and the header hed in each picture pic.

With the use of the picture coding method for generating such streamStr8, however, the compression rate of the stream Str8 is low since eachof the pictures pic included in the group of picture GOP has a headerhed and many of such headers hed have the same value as other headershed. That is to say, the picture coding method for generating a streamStr8 allows a generation of a stream Str8 to which random access can beperformed, on one hand, however, decreases the coding efficiency on theother.

DISCLOSURE OF INVENTION

The present invention is therefore conceived in view of the abovecircumstances, and an object of the present invention is to provide thepicture coding method for coding a picture so that a prompt randomaccess can be operated without reducing the coding efficiency.

In order to achieve the above object, the picture coding methodaccording to the present invention for coding a picture signal on apicture-by-picture basis so as to generate a bit stream comprises: acoding step of coding a parameter set to be used for decoding allpictures included in an access unit made up of a plurality of pictures;and a parameter set placement step of placing, in each access unit inthe bit stream, the parameter set coded in the coding step.

Thus, even in the case of obtaining such bit stream in the middle of thestream, the picture decoding apparatus can decode properly the picturesincluded in the access unit using the parameter set included in theobtained first access unit. As a result, the bit stream can be decodedproperly starting from the access unit. Such bit stream is recorded in arecording medium, therefore, even in the case of performing randomaccess on the bit stream, the picture decoding apparatus can startrandom access promptly, without shifting the position of reading out thedata, from the head of the bit stream to the starting position of therandom access, unlike the conventional example. Moreover, the redundancyof the bit stream can be reduced and the decrease in the codingefficiency can be prevented since the information used for decodingpictures is not placed for each picture in the bit stream.

The picture coding method may further comprise a structureidentification information generation step of generating structureidentification information indicating a placement of the parameter set.

Thus, the placement of the parameter set is indicated in the structureidentification information. The picture decoding apparatus can thereforeexecute random access with a recognition that a precise and promptrandom access can be performed for the bit stream on the access basis,by referring to the structure identification information.

The parameter set includes a plurality of the picture parameter sets,and in the parameter set placement step, a picture parameter set for apicture is placed immediately before the picture in the access unit inthe bit stream, except for a picture parameter set that is alreadyplaced.

Thus, the coded picture parameter set is placed immediately before thecorresponding picture so that each picture parameter set can be codedand sequentially placed, which does not require the storage of the codedpicture parameter sets. Therefore, the picture coding apparatus can bestructured easily.

In the coding step, either any or all of the picture parameter sets arecoded for plural times, and a plurality of same coded picture parametersets are generated, and in the parameter set placement step, theplurality of same picture parameter sets coded in the coding step areplaced in the same access unit.

Thus, a plurality of the same picture parameters are included in theaccess unit, therefore, it is possible to decode the bit stream thuscoded, while preventing the occurrence of errors.

The picture coding apparatus according to the present invention codes apicture signal on a picture-by-picture basis and generating a bit streamand comprises: a coding step of coding a parameter set to be used fordecoding all pictures included in an access unit, except for a picturewhich refers to a picture in another access unit and is not displayedwhen random access is performed, the access unit being made up of aplurality of pictures; and a parameter set placement step of placing, ineach access unit in the bit stream, the parameter set coded in thecoding step.

Thus, the parameter set is included in the bit stream for each accessunit. Therefore, even in the case of obtaining such bit stream in themiddle of the stream, the picture decoding apparatus can decode acurrent picture to be displayed included in the access unit using theparameter set included in the first access unit obtained. Consequently,the bit stream can be decoded starting from the access unit. Such bitstream is recorded in a recording medium. Therefore, even in the case ofperforming random access on the bit stream, the picture decodingapparatus can start random access promptly, without shifting theposition of reading out the data, from the head of the bit stream to thestarting position of the random access, unlike the conventional case.Moreover, the redundancy of the bit stream can be reduced and thedecrease in the coding efficiency can be prevented since the informationused for decoding pictures is not placed for each picture in the bitstream.

The present invention can be realized also as a picture coding apparatusor a program which uses the picture coding method as described above, oreven as a bit stream generated using the picture coding method.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing a structure of the conventionalpicture coding apparatus.

FIG. 2 is a structural diagram showing a structure of the streamoutputted by the conventional picture coding apparatus.

FIG. 3 is a structural diagram showing a structure of the streamaccording to the MPEG-2.

FIG. 4 is a block diagram showing a structure of the picture codingapparatus according to the first embodiment of the present invention.

FIG. 5 is a structural diagram showing the structure of the coded imagesignal outputted by the picture coding apparatus according to the firstembodiment of the present invention.

FIG. 6 is a flowchart showing the picture coding method according to thefirst embodiment of the present invention.

FIG. 7 is an illustration for describing the information outputted fromthe picture coding apparatus according to the first embodiment of thepresent invention.

FIG. 8 is a structural diagram showing a structure of the stream Strthat includes structure identification information according to thefirst embodiment of the present invention.

FIG. 9 is a structural diagram showing a structure of the streamoutputted by the picture coding apparatus according to a first variationdescribed in the first embodiment of the present invention.

FIG. 10 is a flowchart showing an operation of the picture codingapparatus according to the first variation described in the firstembodiment of the present invention.

FIG. 11 is a structural diagram showing a structure of the streamoutputted by the picture coding apparatus according to a secondvariation described in the first embodiment of the present invention.

FIG. 12 is a flowchart showing an operation of the picture codingapparatus according to the second variation described in the firstembodiment.

FIG. 13 is a structural diagram showing a structure of the streamoutputted by the picture coding apparatus according to a third variationof the first embodiment.

FIG. 14A, 14B and 14C are illustrations of a recording medium on which aprogram for realizing the picture coding method according to the firstembodiment of the present invention in a computer system is recorded,according to the second embodiment of the present invention.

FIG. 15 is a block diagram showing a whole structure of a content supplysystem for realizing a content distribution service according to thethird embodiment of the present invention;

FIG. 16 is a diagram showing a cell phone according to the thirdembodiment of the present invention using the picture coding methoddescribed in the first embodiment.

FIG. 17 is a block diagram showing the internal structure of the cellphone according to the third embodiment of the present invention.

FIG. 18 is a structural diagram showing the structure of the digitalbroadcasting system according to the third embodiment of the presentinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

The following describes the embodiments of the present invention withreference to the figures.

First Embodiment

FIG. 4 is a block diagram showing a structure of the picture codingapparatus according to the first embodiment of the present invention.

The picture coding apparatus 100 according to the present embodimentcodes a picture so that a prompt random access can be operated withoutreducing the coding efficiency. More precisely, the picture codingapparatus 100 codes an image signal Vin on a picture-by-picture basisand outputs a stream Str.

The picture coding apparatus 100 includes a motion estimation unit 103,a motion compensation unit 105, a subtractor 106, an orthogonaltransformation unit 107, a quantization unit 108, an inversequantization unit 110, an inverse orthogonal transformation unit 111, anadder 112, a picture memory 104, a switch 113, a variable length codingunit 109, an access point determination unit 102 and a PS memory 101.Each of the components such as the motion estimation unit 103 executesthe following processing per block or per macroblock that constitutes apicture.

The subtractor 106 obtains an image signal Vin, and also, a predictiveimage Pre from the motion compensation unit 105, and calculates adifferential between the image signal Vin and the predictive image Pre.The subtractor 106 then outputs the differential value to the orthogonaltransformation unit 107.

The orthogonal transformation unit 107 transforms the differential valueinto frequency coefficients and outputs them to the quantization unit108.

The quantization unit 108 quantizes the frequency coefficients obtainedfrom the orthogonal transformation unit 107, and outputs the quantizedvalues to the variable length coding unit 109.

The inverse quantization unit 110 restores the quantized values obtainedfrom the quantization unit 108 into the frequency coefficients by meansof inverse quantization, and outputs them to the inverse orthogonaltransformation unit 111.

The inverse orthogonal transformation unit 111 performs inversefrequency transformation on the frequency coefficients outputted fromthe inverse quantization unit 110 in order to transform them into pixeldifferential values, and outputs them to the adder 112.

The adder 112 adds the pixel differential values outputted from theinverse transformation unit 111 and the predictive image Pre outputtedfrom the motion compensation unit 105, so as to generate a decodedimage.

In the case where an instruction to store the decoded image generated bythe adder 112 is received, the switch 113 connects the adder 112 and thepicture memory 104, and allows the decoded image generated by the adder112 to be stored in a picture memory. The decoded image stored in thepicture memory is simply referred to as “picture”.

The motion estimation unit 103 obtains the image signal Vin on amacroblock-by-macroblock basis. The motion estimation unit 103, havingobtained the image signal Vin, refers to the picture stored in thepicture memory 104 as a reference picture, and specifies a picture areathat resembles the obtained image signal Vin the most within thereference picture. The motion estimation unit 103 then estimates amotion vector MV indicating a location of the image area.

The motion estimation unit 103 estimates such motion vector MV in unitsof blocks, each being obtained by further dividing a macroblock. Themotion estimation unit 103, then, by using identification numbers(relative index Idx) for identifying the reference pictures, identifiesthe reference picture that has been referred to among plural referencepicture candidates, based on the picture numbers assigned to each of thepictures stored in the picture memory 104.

The motion compensation unit 105 extracts an image area that is the mostapplicable for the predictive image Pre from among the pictures (decodedimages) stored in the picture memory 104, using the motion vector MVestimated in the above processing as well as the relative index Idx. Themotion compensation unit 105 then generates a predictive image Pre usingthe extracted image area.

The access point determination unit 102 instructs the motion estimationunit 103 and the motion compensation unit 105 to code (intra-picturecode) a predetermined picture as a special picture per predeterminedunit (i.e. random access unit). The access point determination unit 102further outputs an access point identifier rapp indicating that apicture is the special picture to the variable length coding unit 109.

The PS memory 101 obtains the parameter set PS and temporarily storesit. The PS memory 101 then outputs, based on the instruction from theaccess point determination unit 102, a picture parameter set and asequence parameter set of the picture indicated in the instruction fromthe temporarily stored parameter sets PS to the variable length codingunit 109.

The variable length coding unit 109 codes the parameter set PS obtainedfrom outside resources, the motion vector MV, the quantized values, therelative index Idx and the access point identifier rapp. The variablelength coding unit 109 then generates a stream Str by arranging for eachrandom access unit the sequence parameter set as well as the sequenceparameter set included in the coded parameter set PS, and outputs thestream Str.

FIG. 5 is a structural diagram showing a structure of the stream Stroutputted by the picture coding apparatus 100 according to the presentembodiment.

The stream Str includes sequentially from the head a synchronous signalsync, a parameter set PS and plural random access units RAU.

The parameter set PS includes plural sequence parameter sets SPS andplural picture parameter sets PPS.

The random access unit RAU includes sequentially from the head asynchronous signal sync, a single sequence parameter set SPS, pluralpicture parameter sets PPS and plural coded pictures pic. Namely, suchrandom access unit RAU includes all the sequence parameter sets SPS andthe picture parameter sets PPS necessary for decoding all the picturespic included there. Each of the picture parameter set PPS has adifferent value and any one of the picture parameter sets PPS isreferred to by plural pictures pic and used for decoding the pictures.

The picture pic includes sequentially from the head a synchronous signalsync, a parameter set identifier PSID and pixel data pix that is acodeword for pixels of the picture.

The parameter set identifier PSID identifies the parameter sets SPS andPPS to be referred to by the picture from among the parameter sets SPSand PPS included in the random access unit RAU.

FIG. 6 is a flowchart showing a picture coding method of the picturecoding apparatus 100 according to the present embodiment.

The picture coding apparatus 100 firstly judges whether or not a currentpicture to be coded is a random access point, namely, the first picturein the random access unit RAU (Step S100).

When judging that the current picture is a random access point (Y inStep S100), the picture coding apparatus 100 codes the sequenceparameter set SPS (Step S102) and further codes each picture parameterset PPS for all the pictures in the random access unit RAU (Step S103).The picture coding apparatus 100 then places the coded sequenceparameter set SPS and plural picture parameter sets PPS together at thehead side of the random access unit RAU (Step S104).

The picture coding apparatus 100 codes the current picture (Step S106)either after placing the sequence parameter set SPS and the pictureparameter sets PPS in Step S104 or when it is judged that the currentpicture is not a random access point (N in Step S100). The picturecoding apparatus 100 places the coded current picture after the sequenceparameter set SPS and the picture parameter sets PPS mentioned above.Namely, when the parameter sets SPS, PPS mentioned above are arranged inStep S104, the picture coding apparatus 100 places the parameter setsSPS, PPS before any of the pictures pic in the random access unit RAU.When coding the current picture, the picture coding apparatus 100 placesthe parameter set identifier PSID indicating the picture parameter setPPS necessary for decoding the picture pic before the codeword for thepixels of the picture (i.e. pixel data pix) within the coded currentpicture (i.e. picture pic).

After that, the picture coding apparatus 100 judges whether or not anyuncoded pictures are found in the obtained image signal Vin (Step S108).When it is judged that an uncoded picture is found (Y in Step S108), thepicture coding apparatus 100 operates repeatedly the operation startingfrom Step S100. When it is judged that no uncoded pictures are found,namely, when it is judged that all the pictures are coded (N in StepS108), the picture coding apparatus 100 terminates the processing ofcoding. The stream Str is generated using the picture coding method asdescribed above.

Thus, in the picture coding method according to the present embodiment,the stream Str is generated in such a way that the sequence parameterset SPS and the picture parameter sets PPS necessary for decoding(coding) all the pictures included in the random access unit RAU areplaced in the random access unit RAU. The picture decoding apparatustherefore can start decoding properly, namely, can start performingrandom access, by referring to the sequence parameter set SPS and thepicture parameter sets PPS included in the head of the random accessunit RAU in the obtained stream Str, even when the stream Str isobtained in the middle. The picture coding apparatus also does not needto shift a position of reading the data, from the head of the stream Strto the random access point, and thereby, can start performing randomaccess swiftly by omitting the waiting time for the random access, evenwhen random access is performed by reading the stream Str from therecording medium.

In the picture coding method according to the present embodiment, thestream Str, in which the sequence parameter set SPS and the pictureparameter sets PPS are included in each random access unit RAU, isgenerated, therefore, a stream whose bit amount is greater than that ofthe stream Str9 generated using the conventional picture coding methodis generated. However, a header necessary for decoding is not placed perpicture as in the conventional picture coding method according to theMPEG-2. Therefore, the coding efficiency can be further improved withthe present picture coding method compared to the conventional picturecoding method according to the MPEG-2.

The picture coding apparatus 100 according to the present embodiment maygenerate structure identification information indicating a structure ofthe stream Str.

FIG. 7 is an illustration for explaining the information outputted fromthe picture coding apparatus 100.

As shown in FIG. 7, the picture coding apparatus 100 generates structureidentification information sid as an attachment to the stream Str andoutputs it.

The structure identification information sid indicates that the sequenceparameter set SPS and the picture parameter sets PPS are included in allthe random access units RAU in the stream Str. That is to say that it ispossible to perform random access from an arbitrary random access unitRAU in the stream Str.

The picture decoding apparatus, having obtained the stream Str and thestructure identification information sid, can understand easily that theobtained stream Str can be decoded from an arbitrary random access unitRAU based on the structure identification information sid and performrandom access by the fact the picture decoding apparatus attaches suchstructure identification information sid to the stream Str and outputsit.

The picture coding apparatus 100 may include the structureidentification information sid in the stream Str and output it.

FIG. 8 is a structural diagram showing a structure of the stream Strthat includes the structure identification information sid.

As shown in FIG. 8, the picture coding apparatus 100 generates a streamStr in such a way that the structure identification information sid isplaced between a synchronous signal sync and a parameter set PS.

(Variation 1)

The following describes the first variation of the picture codingapparatus according to the present embodiment described above.

The picture coding apparatus according to the first variation outputs astream in which a placement of the picture parameter set PPS isdifferent from the stream Str outputted by the picture coding apparatus100 according to the present embodiment described above.

FIG. 9 is a structural diagram showing a structure of the streamoutputted by the picture coding apparatus according to the presentvariation.

The picture coding apparatus according to the present variation outputsa stream Str1 that includes sequentially from the head a synchronoussignal sync, a parameter set PS and plural random access units RAU1.

The random access unit RAU1 includes sequentially from the head asynchronous signal sync, a sequence parameter set SPS, a pictureparameter set PPS (PPS1) and two pictures pic1, pic2, a pictureparameter set PPS (PPS2) and a picture pic3.

The picture parameter set PPS1 that is necessary for decoding the twopictures pic1 and pic2 is referred to by these pictures in common. Thepicture parameter set PPS2 that is unnecessary for decoding the picturespic 1 and pic2 is not referred to by these pictures. That is to say, thepicture parameter set PPS2 that is necessary for decoding the picturepic3 is referred to by the picture pic3.

The picture parameter set PPS2, being referred to by the picture pic3but not by the pictures pic1 and pic2, does not need to be placed beforethe pictures pic1 and pic2.

The picture parameter PPS1, being referred to by the pictures pic1 andpic2, is already placed immediately before the picture pic1, therefore,does not need to be placed immediately before the picture pic2 again.

Namely, the picture coding apparatus according to the present variationgenerates a stream Str1 so that the picture parameter set PPS referredto by a predetermined picture is placed immediately before thepredetermined picture except for the case in which it is already placed.

FIG. 10 is a flowchart showing the picture coding method employed by thepicture coding apparatus according to the present variation.

The picture coding apparatus firstly judges whether or not a currentpicture to be coded is a random access point, that is, the first picturein the random access unit RAU1 (Step S200).

When judging that the current picture is a random access point (Y inStep S200), the picture coding apparatus codes a sequence parameter setSPS (Step S202) and places it at the head side of the random access unitRAU1 (Step S203). The picture coding apparatus further codes a pictureparameter set PPS of the current picture (Step S204) and places it afterthe sequence parameter set SPS in the random access unit RAU1 (StepS205).

When judging that the current picture is not a random access point (N inStep S200), the picture coding apparatus further judges whether or notthe picture parameter set PPS of the current picture is already codedand is placed after the random access point (Step S206).

When judging in Step S206 that the picture parameter set PPS of thecurrent picture is not coded (N in Step S206), the picture codingapparatus codes the picture parameter set PPS of the current picture andplaces it (Steps S204 and S205).

Either after the placement of the picture parameter set PPS of thecurrent picture performed in Step S205 or when it is judged in Step 206that the picture parameter set PPS of the current picture is alreadycoded (Y in Step S206), the picture coding apparatus codes the currentpicture (Step S208). The picture coding apparatus places the codedcurrent picture (i.e. picture pic) immediately after the correspondingpicture parameter set PPS when coding the current picture after theplacement of the picture parameter set PPS performed in Step S205.Namely, the picture coding apparatus 100 places the picture parameterset PPS immediately before the coded current picture (i.e. picture pic)in the random access unit RAU in the placement of the picture parameterset PPS performed in Step S205. When coding the current picture, thepicture coding apparatus places a parameter set identifier PSID, whichindicates a picture parameter set necessary for decoding the picturepic, before the codeword for the pixels of the picture (i.e. pixel datapix) in the coded current picture (i.e. picture pic).

Then, the picture coding apparatus judges whether or not any uncodedpictures are found in the obtained image signal Vin (Step S210). When itis judged that an uncoded picture is found (Y in Step S210), the picturecoding apparatus executes repeatedly the operation starting from StepS200, and when it is judged that no uncoded pictures are found whichmeans that all the pictures are coded (N in Step S210), the picturecoding apparatus terminates the coding processing. The stream Str1 isgenerated using the picture coding method as described above.

Under the picture coding method employed by the picture coding apparatus100 described above, since it is after the determination, per randomaccess unit RAU, of all the picture parameter sets PPS necessary fordecoding each picture that these picture parameter sets PPS are coded ina group and placed in the head of the random access unit RAU, it isnecessary to temporarily store the determined plural picture parametersPPS.

In contrast, under the picture coding method according to the presentvariation, since the picture parameter sets PPS necessary for decodingthe pictures are sequentially determined per random access unit RAU1 andthe picture parameter sets PPS are coded and then placed in a randomaccess unit, it is not necessary to store the picture parameter sets PPSas mentioned above. Therefore, the structure of the picture codingapparatus according to the present variation can be more simplified thanthat of the picture coding apparatus 100.

In the present embodiment and variation, the sequence parameter set SPScan be modified using a unit superior to the random access unit RAU,therefore, it is enough to place the random access unit RAU for onetime.

(Variation 2)

The following describes the second variation of the picture codingapparatus according to the present embodiment.

The picture coding apparatus according to the second variation outputs astream in which a placement of the sequence parameter set SPS isdifferent from the placement in the stream outputted by the picturecoding apparatus 100 according to the present embodiment describedabove.

FIG. 11 is a structural diagram showing a structure of the streamoutputted by the picture coding apparatus according to the presentvariation.

The picture coding apparatus according to the present variation outputsa stream Str2 that includes sequentially from the head a synchronoussignal sync, a parameter set PS and plural random access unit groupsGRAU.

The random access unit group GRAU includes sequentially from the head asequence parameter set SPS and plural random access units RAU2. Namely,the random access unit group GRAU is constructed as a unit assemblingplural random access units RAU2 for the convenience of storage andtransmission.

The sequence parameter set SPS is a parameter which can be modifiedusing a unit superior to the random access unit RAU2. Therefore, themodification does not necessarily need to be made for each random accessunit RAU2. Normally, only several sequence parameter sets SPS arerequired in the stream, and in many cases, only one sequence parameterset is enough.

The picture coding apparatus according to the present variation does notplace a sequence parameter set SPS for each random access unit RAU2, butfor each random access unit group GRAU, that is, to place a singlesequence parameter set SPS in the head of each random access unit groupGRAU.

The random access unit group GRAU includes a sequence parameter set SPSand a picture parameter set PPS which are necessary for decoding all thepictures included in it, therefore, the random access unit group GRAU isidentifiable as the random access unit RAU or RAU1 according to theembodiment and the variation 1 described above. The RAU2 included insuch random access unit group GRAU can be regarded as a subunit obtainedby dividing the random access unit group GRAU.

FIG. 12 is a flowchart showing an operation of the picture codingapparatus according to the present variation.

The picture coding apparatus firstly judges whether or not a currentpicture to be coded is the first picture included in the random accessunit group GRAU (Step S300).

When judging that the current picture is the first picture (Y in StepS300), the picture coding apparatus codes a sequence parameter set SPS(Step S302) and places it at the head side of the random access unitgroup GRAU (Step S303). The picture coding apparatus further codes thepicture parameter set PPS of the current picture (Step S304) and placesit at the head side of the random access unit RAU2 (Step S305).

When judging that the current picture is not the first picture includedin the random access unit group GRAU (N in Step S300), the picturecoding apparatus further judges whether or not the picture parameter setPPS of the current picture is already coded and is placed after therandom access point (i.e., a head of the random access unit RAU2) (StepS306).

When it is judged in Step S306 that the picture parameter set PPS of thecurrent picture is not coded (N in Step S306), the picture codingapparatus codes the picture parameter set PPS of the current picture andplaces it (Steps S304 and S305).

Either after the placement of the picture parameter set PPS performed inStep S305 or when judging in Step S306 that the picture parameter setPPS of the current picture is already coded (N in Step S 306), thepicture coding apparatus codes the current picture (Step S308).

The picture coding apparatus then judges whether or not any uncodedpictures are found in the obtained image signal Vin (Step S310). Whenjudging that an uncoded picture is found (Y in Step S310), the picturecoding apparatus executes repeatedly the operation starting from StepS300. When judging that no uncoded pictures are found (N in Step S310),the picture coding apparatus terminates the coding processing. Thestream Str2 in which only one sequence parameter set SPS is included ineach random access unit group GRAU is generated using the picture codingmethod described above.

Thus, the picture coding apparatus according to the present variationgenerates the stream Str2 in which a single sequence parameter set SPSis placed for plural random access units RAU2. The bit amount includedin the stream Str2 therefore can be reduced more than the bit amountincluded in the stream Str generated by the picture coding apparatus 100described above.

In the variations 1 and 2 described in the present embodiment, a codedparameter set PS (i.e. PPSs and SPSs) is placed at the head side of thestream, however, it may not be placed as such since it is placed, asnecessary, in each random access unit RAU.

(Variation 3)

The following describes the third variation of the picture codingapparatus according to the present embodiment described above.

The picture coding apparatus according to the third variation generatesand outputs a stream different from the stream outputted by the picturecoding apparatus 100 according to the present embodiment describedabove.

FIG. 13 is a structural diagram showing a structure of the streamoutputted by the picture coding apparatus according to the presentvariation.

The picture coding apparatus according to the present variation outputsa stream Str3 that includes sequentially from the head a synchronoussignal sync and plural random access units RAU (RAU0, RAU01, RAU02, . .. ).

The random access unit RAU01 includes sequentially from the head asynchronous signal sync, a parameter set PS (PS1), pictures pic1, pic2and pic3. The random access unit RAU2 includes sequentially from thehead a synchronous signal sync, random access point information RPS, aparameter set PS (PS2), pictures pic4, pic5 and pic6.

For example, the picture pic1 is an I-picture that is intra-picturecoded whereas the picture pic2 is a P-picture that is coded withreference to the picture pic1. The picture pic3 is a B-picture that iscoded with reference to the pictures pic1 and pic2. The picture pic4 isan I-picture that is intra-picture coded whereas the picture pic5 is aB-picture that is coded with reference to the pictures pic2 and pic4.The picture pic6 is a B-picture that is coded with reference to thepicture pic4 and other pictures in the random access unit RAU02.

The parameter set PS1 includes a sequence parameter set, pictureparameter sets for the pictures pic2 and pic3 and a picture parameterset for the picture pic5 that is included in the random access unitRAU02.

Namely, the picture pic2 is decoded with reference to the parameter setPS1 and the picture pic1 whereas the picture pic3 is decoded withreference to the parameter set PS1 and the pictures pic1 and pic2, whenrandom access is performed on the stream Str3 starting from the randomaccess unit RAU01. Then, the picture pics included in the random accessunit RAU02 is decoded with reference to the parameter set PS1 and thepictures pic2 and pic4 whereas the picture pic6 is decoded withreference to the parameter set PS2, the picture pic4 and other picturesincluded in the random access unit RAU02.

When random access is performed on the stream Str3 starting from therandom access unit RAU02, the picture pic5 is neither decoded nordisplayed whereas the pictures pic4 and pic6 are sequentially decodedand then displayed.

Namely, there is no need to place the picture parameter set necessaryfor the picture pic5 in the random access unit RAU02 since the decodingof the picture pic5, a B-picture, included in the random access unitRAU02 needs to refer to the pictures included in the previous randomaccess unit RAU01. Even when random access is performed on the streamStr3 starting from the random access unit RAU02, the picture pic5 is notdecoded. Therefore, there is no need to place, in the random access unitRAU02, the picture parameter set necessary for the picture pic5, asdescribed above.

In the variations 1-3 of the present embodiment described above, aparameter set identifier PSID is included in the stream on apicture-by-picture basis. However, when the picture is composed ofplural slices, a parameter set identifier PSID may be included on aslice-by-slice basis.

The random access unit shown in the embodiment and the variations 1-3described above does not necessarily have to be a group of picturesincluding a picture of the special type defined by the JVT. It may be agroup of pictures including simply an intra-picture coded picture(I-picture) in the head because of the fact that a parameter set PS isplaced for each random access unit RAU as necessary.

Furthermore, in the embodiment and the variations 1-3 described above, asingle sequence parameter set SPS and plural picture parameter sets PPSthat are different from one another are coded for one time and placedfor each random access unit RAU or each random access unit group GRAU.By performing coding on these parameter sets for plural times, however,a plurality of the same coded sequence parameter sets SPS and aplurality of the same coded picture parameter sets PPS may be placed foreach random access unit RAU or each random access unit group GRAU.Consequently, errors can be prevented, for example, at the time ofdecoding.

Second Embodiment

Furthermore, the processing illustrated in the above embodiment can becarried out easily in an independent computer system by recording aprogram for realizing the picture coding method described in the aboveembodiment onto a recording medium such as a flexible disk or the like.

FIGS. 14A, 14B and 14C are illustrations of a recording medium, on whicha program for carrying out the picture coding method described in thefirst embodiment in the computer system is recorded.

FIG. 14B shows a full appearance of a flexible disk FD, its structure atcross section and a full appearance of the disk itself FD1 as a mainbody of a recording medium whereas FIG. 14A shows an example of aphysical format of the flexible disk FD1.

The disk FD1 is contained in a case F with a plurality of tracks Trformed concentrically from the periphery to the inside on the surface ofthe disk FD1, and each track is divided into 16 sectors Se in theangular direction. Thus, the picture coding method as the programmentioned above is recorded in an area assigned for it on the disk FD1.

FIG. 14C shows a structure for recording and reading out the program onthe flexible disk FD.

When the program is recorded on the flexible disk FD, the computersystem Cs writes in the picture coding method as the program mentionedabove via a flexible disk drive FDD. When the picture coding method isconstructed in the computer system Cs using the program on the flexibledisk FD, the program is read out from the flexible disk FD and thentransferred to the computer system Cs by the flexible disk drive FDD.

In the above explanation, the flexible disk FD is used as an example ofa recording medium, but the same processing can also be performed usingan optical disk. In addition, the recording medium is not limited tothese mentioned above, but any other medium capable of recording aprogram such as an IC card and a ROM cassette can be employed.

Third Embodiment

The following is a description for the application of the picture codingmethod illustrated in the above-mentioned embodiment and a system usingthe method.

FIG. 15 is a block diagram showing an overall configuration of a contentsupply system ex100 for realizing content delivery service. The area forproviding communication service is divided into cells of desired size,and cell sites ex107-ex110, which are fixed wireless stations, areplaced in respective cells.

This content supply system ex100 is connected to apparatuses such as acomputer ex111, a Personal Digital Assistant (PDA) ex112, a cameraex113, a cell phone ex114 and a cell phone with a camera ex115 via, forexample, Internet ex101, an Internet service provider ex102, a telephonenetwork ex104, as well as the cell sites ex107-ex110.

However, the content supply system ex100 is not limited to theconfiguration shown in FIG. 15 and may be connected to a combination ofany of them. Also, each apparatus may be connected directly to thetelephone network ex104, not through the cell sites ex107-ex110.

The camera ex113 is an apparatus capable of shooting video such as adigital video camera. The cell phone ex114 may be a cell phone of any ofthe following system: a Personal Digital Communications (PDC) system, aCode Division Multiple Access (CDMA) system, a Wideband-Code DivisionMultiple Access (W-CDMA) system or a Global System for MobileCommunications (GSM) system, a Personal Handyphone System (PHS) or thelike.

A streaming server ex103 is connected to the camera ex113 via thetelephone network ex104 and also the cell site ex109, which realizes alive distribution or the like using the camera ex113 based on the codeddata transmitted from the user. Either of the camera ex113, the serverwhich transmits the data and the like may code the data. The movingpicture data shot by a camera ex116 may be transmitted to the streamingserver ex103 via the computer ex111. In this case, either the cameraex116 or the computer ex111 may code the moving picture data. An LSIex117 included in the computer ex111 and the camera ex116 performs thecoding processing. Software for coding and decoding pictures may beintegrated into any type of recording medium (such as a CD-ROM, aflexible disk and a hard disk) that is a recording medium which isreadable by the computer ex111 or the like. Furthermore, a cell phonewith a camera ex115 may transmit the moving picture data. This movingpicture data is the data coded by the LSI included in the cell phoneex115.

The content supply system ex100 codes contents (such as a music livevideo) shot by a user using the camera ex113, the camera ex116 or thelike in the same way as shown in the above-mentioned embodiment andtransmits them to the streaming server ex103, while the streaming serverex103 makes stream delivery of the content data to the clients at theirrequests. The clients include the computer ex111, the PDA ex112, thecamera ex113, the cell phone ex114 and so on capable of decoding theabove-mentioned coded data. In the content supply system ex100, theclients can thus receive and reproduce the coded data, and can furtherreceive, decode and reproduce the data in real time so as to realizepersonal broadcasting.

When each apparatus in this system performs coding or decoding, thepicture coding apparatus or the picture decoding apparatus shown in theabove-mentioned embodiment can be used.

A cell phone will be explained as an example of such apparatus.

FIG. 16 is a diagram showing the cell phone ex115 using the picturecoding method explained in the above-mentioned embodiment. The cellphone ex115 has an antenna ex201 for communicating with the cell siteex110 via radio waves, a camera unit ex203 such as a CCD camera capableof shooting moving and still pictures, a display unit ex202 such as aliquid crystal display for displaying the data such as decoded picturesand the like shot by the camera unit ex203 or received by the antennaex201, a body unit including a set of operation keys ex204, a voiceoutput unit ex208 such as a speaker for outputting voice, a voice inputunit ex205 such as a microphone for inputting voice, a recording mediumex207 for recording coded or decoded data such as data of moving orstill pictures shot by the camera, data of received e-mails and that ofmoving or still pictures, and a slot unit ex206 for attaching therecording medium ex207 to the cell phone ex115. The recording mediumex207 stores in itself a flash memory element, a kind of ElectricallyErasable and Programmable Read Only Memory (EEPROM) that is anonvolatile memory electrically erasable from and rewritable to aplastic case such as an SD card.

Next, the cell phone ex115 will be explained with reference to FIG. 17.In the cell phone ex115, a main control unit ex311, designed in order tocontrol overall each unit of the main body which contains the displayunit ex202 as well as the operation keys ex204, is connected mutually toa power supply circuit unit ex310, an operation input control unitex304, a picture coding unit ex312, a camera interface unit ex303, aLiquid Crystal Display (LCD) control unit ex302, a picture decoding unitex309, a multiplexing/demultiplexing unit ex308, a read/write unitex307, a modem circuit unit ex306 and a voice processing unit ex305 viaa synchronous bus ex313.

When a call-end key or a power key is turned ON by a user's operation,the power supply circuit unit ex310 supplies the respective units withpower from a battery pack so as to activate the digital cell phone witha camera ex115 as a ready state.

In the cell phone ex115, the voice processing unit ex305 converts thevoice signals received by the voice input unit ex205 in conversationmode into digital voice data under the control of the main control unitex311 including a CPU, ROM and RAM, the modem circuit unit ex306performs spread spectrum processing for the digital voice data, and thecommunication circuit unit ex301 performs digital-to-analog conversionand frequency conversion for the data, so as to transmit it via theantenna ex201. Also, in the cell phone ex115, the communication circuitunit ex301 amplifies the data received by the antenna ex201 inconversation mode and performs frequency conversion and theanalog-to-digital conversion to the data, the modem circuit unit ex306performs inverse spread spectrum processing of the data, and the voiceprocessing unit ex305 converts it into analog voice data so as to outputit via the voice output unit ex208.

Furthermore, when transmitting an e-mail in data communication mode, thetext data of the e-mail inputted by operating the operation keys ex204of the main body is sent out to the main control unit ex311 via theoperation input control unit ex304. In the main control unit ex311,after the modem circuit unit ex306 performs spread spectrum processingof the text data and the communication circuit unit ex301 performs thedigital-to-analog conversion and the frequency conversion for the textdata, the data is transmitted to the cell site ex110 via the antennaex201.

When picture data is transmitted in data communication mode, the picturedata shot by the camera unit ex203 is supplied to the picture codingunit ex312 via the camera interface unit ex303. When it is nottransmitted, it is also possible to display the picture data shot by thecamera unit ex203 directly on the display unit ex202 via the camerainterface unit ex303 and the LCD control unit ex302.

The picture coding unit ex312, which includes the picture codingapparatus as described for the present invention, compresses and codesthe picture data supplied from the camera unit ex203 using the codingmethod employed by the picture coding apparatus as shown in theembodiment mentioned above so as to transform it into coded image data,and sends it out to the multiplexing/demultiplexing unit ex308. At thistime, the cell phone ex115 sends out the voice received by the voiceinput unit ex205 during the shooting with the camera unit ex203 to themultiplexing/demultiplexing unit ex308 as digital voice data via thevoice processing unit ex305.

The multiplexing/demultiplexing unit ex308 multiplexes the coded imagedata supplied from the picture coding unit ex312 and the voice datasupplied from the voice processing unit ex305, using a predeterminedmethod, then the modem circuit unit ex306 performs spread spectrumprocessing of the multiplexed data obtained as a result of themultiplexing, and lastly the communication circuit unit ex301 performsdigital-to-analog conversion and frequency transform of the data for thetransmission via the antenna ex201.

As for receiving data of a moving picture file which is linked to a Webpage or the like in data communication mode, the modem circuit unitex306 performs inverse spread spectrum processing for the data receivedfrom the cell site ex110 via the antenna ex201, and sends out themultiplexed data obtained as a result of the inverse spread spectrumprocessing.

In order to decode the multiplexed data received via the antenna ex201,the multiplexing/demultiplexing unit ex308 demultiplexes the multiplexeddata into a bit stream of image data and that of voice data, andsupplies the coded image data to the picture decoding unit ex309 and thevoice data to the voice processing unit ex305, respectively via thesynchronous bus ex313.

Next, the picture decoding unit ex309, including the picture decodingapparatus as described for the present invention, decodes the bit streamof the image data using the decoding method corresponding to the codingmethod as shown in the above-mentioned embodiments to generatereproduced moving picture data, and supplies this data to the displayunit ex202 via the LCD control unit ex302, and thus the image dataincluded in the moving picture file linked to a Web page, for instance,is displayed. At the same time, the voice processing unit ex305 convertsthe voice data into analog voice data, and supplies this data to thevoice output unit ex208, and thus the voice data included in the movingpicture file linked to a Web page, for instance, is reproduced.

The present invention is not limited to the above-mentioned system sinceground-based or satellite digital broadcasting has been in the newslately and at least either the picture coding apparatus or the picturedecoding apparatus described in the above-mentioned embodiment can beincorporated into a digital broadcasting system as shown in FIG. 18.More specifically, a bit stream of video information is transmitted froma broadcast station ex409 to or communicated with a broadcast satelliteex410 via radio waves. Upon receipt of it, the broadcast satellite ex410transmits radio waves for broadcasting. Then, a home-use antenna ex406with a satellite broadcast reception function receives the radio waves,and a television (receiver) ex401 or a set top box (STB) ex407 decodes acoded bit stream for reproduction. The picture decoding apparatus asshown in the above-mentioned embodiment can be implemented in thereproducing apparatus ex403 for reading out and decoding the bit streamrecorded on a recording medium ex402 such as a CD and a DVD. In thiscase, the reproduced moving picture signals are displayed on a monitorex404. It is also conceivable to implement the picture decodingapparatus in the set top box ex407 connected to a cable ex405 for acable television or the antenna ex406 for satellite and/or ground-basedbroadcasting so as to reproduce them on a monitor ex408 of thetelevision ex401. The picture decoding apparatus may be incorporatedinto the television, not in the set top box. Also, a car ex412 having anantenna ex411 can receive signals from the satellite ex410 or the cellsite ex107 for replaying moving picture on a display device such as acar navigation system ex413 set in the car ex412.

Furthermore, the picture coding apparatus as shown in theabove-mentioned embodiment can code picture signals and record them onthe recording medium. As a concrete example, a recorder ex420 such as aDVD recorder for recording picture signals on a DVD disk ex421, a diskrecorder for recording them on a hard disk can be cited. They can berecorded on an SD card ex422. When the recorder ex420 includes thepicture decoding apparatus as shown in the above-mentioned embodiment,the picture signals recorded on the DVD disk ex421 or the SD card ex422can be reproduced for display on the monitor ex408.

As for the structure of the car navigation system ex413, the structurewithout the camera unit ex203, the camera interface unit ex303 and thepicture coding unit ex312, out of the components shown in FIG. 17, isconceivable. The same applies for the computer ex111, the television(receiver) ex401 and others.

In addition, three types of implementations can be conceived for aterminal such as the cell phone ex114: a sending/receiving terminalimplemented with both an encoder and a decoder, a sending terminalimplemented with an encoder only, and a receiving terminal implementedwith a decoder only.

As described above, it is possible to use the picture coding methoddescribed in the above-mentioned embodiment for any of theabove-mentioned apparatuses and systems, and by thus doing, the effectsdescribed in the above-mentioned embodiment can be obtained.

From the invention thus described, it will be obvious that theembodiments of the invention may be varied in many ways. Such variationsare not to be regarded as a departure from the spirit and scope of theinvention, and all such modifications as would be obvious to one skilledin the art are intended for inclusion within the scope of the followingclaims.

INDUSTRIAL APPLICABILITY

The picture coding method according to the present invention allowscoding of pictures so that random access can be performed withoutreducing the coding efficiency. The present picture coding method can beemployed by a picture coding apparatus, such as a video camera, a cellphone with a recording function, or the like, which codes pictures usingthe method.

1. A picture coding method for coding a picture signal on apicture-by-picture basis so as to generate a bit stream, the methodcomprising: a coding step of coding a parameter set to be used fordecoding all pictures included in an access unit made up of a pluralityof pictures ; and a parameter set placement step of placing, in eachaccess unit in the bit stream, the parameter set coded in the codingstep.
 2. The picture coding method according to claim 1, wherein theparameter set includes picture parameter sets to be used for decodingone or more pictures, and the picture coding method further comprises aparameter identification information placement step of placing parameteridentification information before a codeword for pixels of a picture inthe bit stream, the parameter identification information indicating apicture parameter set for the picture.
 3. The picture coding methodaccording to claim 2, wherein in the parameter set placement step, theparameter set is placed before any of the pictures in the access unit inthe bit stream.
 4. The picture coding method according to claim 3,further comprising a structure identification information generationstep of generating structure identification information indicating aplacement of the parameter set.
 5. The picture coding method accordingto claim 2, wherein the parameter set includes: a plurality of thepicture parameter sets; and a sequence parameter set to be used incommon for decoding all the pictures included in the access unit, and inthe parameter set placement step, the sequence parameter set is placedin a head side of the access unit in the bit stream, and a pictureparameter set for a picture included in a sub access unit is placed inthe sub access unit in the bit stream, the sub access unit beingobtained by dividing the access unit.
 6. The picture coding methodaccording to claim 5, further comprising a structure identificationinformation generation step of generating structure identificationinformation indicating a placement of the parameter set.
 7. The picturecoding method according to claim 6, wherein in the structureidentification information generation step, the structure identificationinformation is generated and then included in the bit stream.
 8. Thepicture coding method according to claim 6, wherein in the structureidentification information generation step, the structure identificationinformation is generated and then attached to the bit stream.
 9. Thepicture coding method according to claim 2, wherein the parameter setincludes a plurality of picture parameter sets, and in the parameter setplacement step, a picture parameter set for a picture is placed beforethe picture in the access unit in the bit stream.
 10. The picture codingmethod according to claim 9, wherein in the parameter set placementstep, a picture parameter set for a picture is placed immediately beforethe picture in the access unit in the bit stream, except for a pictureparameter set that is already placed.
 11. The picture coding methodaccording to claim 9, wherein in the coding step, either any or all ofthe picture parameter sets are coded for plural times, and a pluralityof same coded picture parameter sets are generated, and in the parameterset placement step, the plurality of same picture parameter sets codedin the coding step are placed in the same access unit.
 12. The picturecoding method according to claim 11, wherein the parameter set includesa sequence parameter set to be used in common for decoding all thepictures included in the access unit, in the coding step, the sequenceparameter set is coded for plural times, and a plurality of same codedsequence parameter sets are generated, and in the parameter setplacement step, the plurality of same sequence parameter sets coded inthe coding step are placed in the same access unit.
 13. A picture codingmethod for coding a picture signal on a picture-by-picture basis so asto generate a bit stream, the method comprising: a coding step of codinga parameter set to be used for decoding all pictures included in anaccess unit, except for a picture that refers to a picture in anotheraccess unit and is not displayed when random access is performed, theaccess unit being made up of a plurality of pictures; and a parameterset placement step of placing, in each access unit in the bit stream,the parameter set coded in the coding step.
 14. A bit stream thatincludes a plurality of access units which is obtained by coding apicture signal on a picture-by-picture basis, the access unit being madeup of a plurality of coded pictures, wherein a parameter set is placedin the access unit, the parameter set being used for decoding all thepictures included in the access unit.
 15. The bit stream according toclaim 14, wherein the parameter set is placed before any of the picturesin the access unit.
 16. The bit stream according to claim 14, whereinthe parameter set includes: a plurality of picture parameter sets to beused for decoding one or more pictures; and a sequence parameter set tobe used in common for decoding all the pictures included in the accessunit, the sequence parameter set is placed in a head side of the accessunit, and a picture parameter set for a picture included in a sub accessunit, out of the plurality of picture parameter sets, is placed in thesub access unit, the sub access unit being obtained by dividing theaccess unit.
 17. The bit stream according to claim 16, wherein the bitstream includes structure identification information indicating aplacement of the parameter set.
 18. The bit stream according to claim16, wherein structure identification information is attached to the bitstream, the information indicating a placement of the parameter set. 19.The bit stream according to claim 14, wherein the parameter set includesa plurality of picture parameter sets to be used for decoding one ormore pictures, and each of the picture parameter sets is placed beforethe corresponding picture.
 20. The bit stream according to claim 19,wherein the picture parameter set is placed immediately before thecorresponding picture, except for a case in which the picture parameterset is already placed in a head side of the access unit.
 21. A programfor coding a picture signal on a picture-by-picture basis so as togenerate a bit stream, the program causing a computer to execute thefollowing: a coding step of coding a parameter set to be used fordecoding all pictures included in an access unit made up of a pluralityof pictures; and a parameter set placement step of placing, in eachaccess unit in the bit stream, the parameter set coded in the codingstep.
 22. The program according to claim 21, wherein the parameter setincludes: a plurality of picture parameter sets to be used for decodingone or more pictures; and a sequence parameter set to be used in commonfor decoding all the pictures included in the access unit, in theparameter set placement step, the sequence parameter set is placed in ahead side of the access unit in the bit stream, and a picture parameterset for a picture included in a sub access unit is placed in the subaccess unit in the bit stream, the sub access unit being obtained bydividing the access unit.
 23. A picture coding apparatus for coding apicture signal on a picture-by-picture basis so as to generate a bitstream, the apparatus comprising: a coding unit operable to code aparameter set to be used for decoding all pictures included in an accessunit made up of a plurality of pictures; and a parameter set placementunit operable to place, in each access unit in the bit stream, theparameter set coded by the coding unit.